docs: def export(self, nidm_version, export_dir):
          """
          Create prov graph.
          """
          attributes = [(PROV['type'], NIDM_STATISTIC_MAP),
                        (DCT['format'], self.fmt)]
  
          if not self.isderfrommap:
              attributes.insert(0, (
                  NIDM_IN_COORDINATE_SPACE,  self.coord_space.id))
              attributes.insert(0, (PROV['label'], self.label))
  
          if not self.stat_type == 'Z':
              attributes.insert(0, (NIDM_ERROR_DEGREES_OF_FREEDOM, self.dof))
              attributes.insert(0, (NIDM_EFFECT_DEGREES_OF_FREEDOM, self.effdof))
          else:
              # For Z-Statistic error dof is infinity and effect dof is 1
              attributes.insert(0, (NIDM_ERROR_DEGREES_OF_FREEDOM, float("inf")))
              attributes.insert(0, (NIDM_EFFECT_DEGREES_OF_FREEDOM, self.effdof))
  
          if self.stat is not None:
              attributes.insert(0, (NIDM_STATISTIC_TYPE, self.stat))
  
          if self.contrast_name is not None:
              attributes.insert(0, (NIDM_CONTRAST_NAME, self.contrast_name))
  
          # Create "Statistic Map" entity
          # FIXME: Deal with other than t-contrast maps: dof + statisticType
          self.add_attributes(attributes)